1. Field of the Invention
The present invention relates to an image pick-up apparatus, a method of white balance control and a program for white balance control.
2. Description of the Related Art
In most of conventional digital cameras or image pick-up apparatuses, an image of an object photographed or obtained using a solid state image pick-up element such as CCD is displayed as a through (finder) image on a liquid crystal display monitor independently of a shutter operation by a user. In this sort of digital camera, a white balance has to be adjusted for faithfully reproducing colors of the object. The white balance is adjusted to photograph a white object in a white color even in case that the object is photographed under various lights of different color temperatures. The white balance is secured by adjusting gains of an image signal output from the solid state image pick-up element, that is, by adjusting gains respectively for R color component, G color component and B color component of the image signal depending on the surroundings (light source) for photographing the object (photographing surroundings). Therefore, if gain-correction coefficients used as gain values and standards for plural sorts of expected photographing surroundings are prepared and stored in a memory in advance, the user can near-perfectly adjust the white balance of the image that he or she is going to photograph by using these gain-correction coefficients depending on the photographing surroundings. The white balance adjusting operation mentioned above requires the user to make troublesome operation, and therefore an automatic function for automatically adjusting the white-balance has been proposed. In a general technique for adjusting the white balance, a light source in the photographing surrounding where a through image is photographed, is judged based on the color temperatures of the through image and the like, and gains for R component and B component contained in image data are adjusted based on the judged light source (for example, refer to a Patent Document #1).
A conventional technique is also used, which detects a flicker based on an image obtained by CCD to judge the light source, and determines that the light source is a fluorescent lamp when the flicker is detected.
[Patent Document #1] Japanese Laid-Open Patent Specification No. 2003-264850
However, to detect the flicker in the image data obtained by CCD as described above, it is necessary to obtain about 30 photographs per second. Therefore, when a picture is taken in a dark surrounding such as in a room, the number of photographs taken in a second is reduced by the automatic exposure function (AE function), and therefore it is difficult to detect the flicker of the fluorescent lamp, resulting in failure in correctly determining the light source. In general, since a cover glass of the image pick-up optical system and CCD is provided with a filtering function for filtering the infrared rays, it is hard to determine whether the light source is an incandescent lamp or not by detecting the infrared rays from the image obtained by CCD. Therefore, it is not possible to control the white balance by using CCD which is one of conventional sensors in the image pick-up apparatus.
The present invention has been made in consideration of the above mentioned problems, and has an object to provide an image pick-up apparatus which can control the white balance by effectively using conventionally available sensors in the conventional image pick-up apparatus, a white balance control method, and a program for controlling the white balance.